DVT can be a very serious condition having a potential for fatality by causing a pulmonary embolism and it is a post-operative risk associated, although not exclusively so, with hip joint replacement surgery. It is therefore desirable that such surgery should be accompanied by application of a screening procedure to detect DVT but there is no existing procedure well suited to such use.
DVT is diagnosable by venography to a high level of accuracy and reliability. However, this conventionally involves a radiological procedure employing application of contrast media and is not best suited to the general usage which screening entails, but rather represents a good choice of confirmatory procedure to be applied in the event of a positive screening result.
Another procedure applicable to DVT diagnosis is based on ultrasound scanning, but this also is not best suited to screening use as it is complex.
Impedance plethysmography or so-called IPG is yet another procedure applicable to DVT detection but is found to require a very careful technique in practical application and is, again, inappropriate for use in screening. Development of the present invention was in fact preceded by a study of IPG to assess its potential for use in DVT screening, which study is described by J. G. Brown et al in J. Bone and Joint Surg. 69-B: 264-267, May 1987.